The invention relates to the field of dietetic lipids, in particular for infant formulas. It relates to a lipid composition which is close to that of human milk.
Human milk fat is composed essentially of triacylglycerols (TAGs) whose fatty acid structure, composition and distribution are specific. It is characterized in particular by the presence of two long-chain polyunsaturated fatty acids (LC-PUFA), arachidonic acid (AA, C20:4, n-6) and docosahexaenoic acid (DHA, C22:6, n-3) predominantly at the 2-position of the triacylglycerol, by the abundance of saturated (SFA) palmitic acid. (P, C16:0) and by the fact that P is predominantly at the 2-position of the triacylglycerol.
Lipid compositions for infant formulas which mimic human milk fat as well as processes for the preparation of such compositions are described in patent EP-B-209327 and in patent applications WO 94/26855 (PCT/EP 94/01306) and WO 94/26854 (PCT/EP 94/01304). These compositions comprise a mixture of TAGs in which more than 50% of the fatty acids at the 2-position of the triacylglycerol are SFAs, predominantly P, and where the fatty acids at the 1,3-positions of the triacylglycerol comprise medium-chain C.sub.8 -C.sub.14 unsaturated fatty acids and saturated fatty acids (MCFA).
The process for preparing these compositions, which is described in EP-B-209327, consists in an interesterification, catalysed by a 1,3-regiospecific lipase of a mixture consisting, on the one hand, of a palm oil fraction comprising 80% of tristearin and 20% of 1,3-dipalmitoyl-2-olein and, on the other hand, of a mixture of free fatty acids containing a substantial quantity of unsaturated fatty acids. Under the action of the 1,3-regiospecific lipase, medium-chain unsaturated and/or saturated fatty acid residues are introduced at the 1,3-positions of the 2-palmitoyl-glycerides. The free fatty acids of the crude mixture are then removed by steam distillation. The mixture of synthetic TAGs produced is finally mixed with various vegetable oils.
In WO 94/26855, the above mixture of synthetic TAGs, mixed with various vegetable oils in defined portions, is subjected to an interesterification using a 1,3-regiospecific lipase.
In WO 94/26854, where appropriate, after removal of the diglycerides by enzymatic treatment, the trisaturated TAGs are partially removed from the above mixture of synthetic TAGs by interesterification using a 1,3-regiospecific lipase in the presence of an oil which is high in mono- or diunsaturated acids.
The known processes have disadvantages.
Since most of the customary lipases have a low reactivity towards polyunsaturated fatty acids (PUFAs), particularly towards the LC-PUFAs, it is very difficult to incorporate the desired quantities of these fatty acids, in particular of DHA into the TAGs using a 1,3-regiospecific lipase. Thus, to achieve an appreciable degree of incorporation, it is necessary to use a large excess of fatty acid, for example in concentrated form, and a long reaction time. Concentrates of PUFAs are very expensive. The long reaction time can cause significant oxidation of the PUFAs which are particularly sensitive to oxidation when they are in the form of free fatty acids. Such an oxidation reduces the nutritional value of the PUFAs and may produce degradation compounds which are health hazards. PA1 Furthermore, the use of 1,3-regiospecific lipase produces trisaturated TAGs in excess and also diglycerides. Subsequent enzymatic treatments are required, in particular to remove the trisaturated TAGs in excess from the crude product, which makes the process complicated and expensive. PA1 Finally, the lipid mixture obtained must, in spite of everything, be mixed with other fats in order to correspond to the composition of human milk fat. PA1 it contains less than 2% by weight of free fatty acids, PA1 the fatty acids of the triacylglycerols comprise, by weight: PA1 palmitic acid is predominantly at the 2-position of the triacylglycerols and arachidonic and docosahexaenoic acids are distributed between the 1-, 2- and 3-positions of the triacylglycerols.